Chip cards are widespread and are used in a large number of applications. In security-related applications, chip cards are used as keys, for example. In cashless payment transactions, information with a monetary value can be stored on a chip card. One exemplary application of this is a cash card. The aforementioned applications, inter alia, require that the data which are stored on the chip card and the chip itself are protected against attacks and manipulations.
If necessary, physical attacks involve parts of the chip being removed in order to spy out a circuit integrated on the chip. In addition, signals can be tapped off in order to read data, which is called “probing”. It is also conceivable for signals to be deliberately applied to lines in the integrated circuit from outside in order to manipulate the operation of the integrated circuit such that it is possible to read security-related data or in order to ascertain the way in which the integrated circuit works on the basis of a circuit reaction. This procedure is called “forcing”.
Previous protective mechanisms against such attacks have been implemented on the chip itself. To protect against physical attacks, the chip comprises a shield which is arranged over the actual integrated circuit. The nature of the protection by the shield may either be active or passive.
A passive shield comprises a track-like or laminar structure which covers the underlying circuit arrangement in order to prevent attacks through simple spying and to at least make it difficult to access suitable points of attack for probing or forcing.
An active shield comprises a conductor structure which covers the circuit arrangement and to which a voltage or a signal is applied. When this shield is destroyed, an accompanying change or interruption in the voltage or in the signal is detected. Voltage or signal changes which accompany manipulations, for example by means of probing or forcing, can also be detected. Following detection, it is possible to initiate suitable defense measures, for example shutting down the circuit operation or erasure operations in registers in the circuit arrangement.
Such shields are accompanied by additional cost involvement because a further metallized layer on the circuit arrangement or a larger area needs to be provided.